The long-term objectives of the proposed research are to improve our understanding of the molecular bases of inherited retinal degenerations (IRDs) so that therapies can be developed for these blinding disorders. IRDs are characterized by progressive dysfunction and death of photoreceptor cells, and occur in non-syndromic and syndromic forms. IRDs are genetically heterogeneous, with over 140 disease genes identified to date. However, the identified mutations account for only ~50% of patients with these disorders and the mechanisms by which the majority of the identified mutations cause photoreceptor cell death remain to be determined. The Aims of the proposed research are based on the recognition that photoreceptor outer segments are specialized sensory cilia. Work on retinitis pigmentosa 1 (RP1) lead the applicant to appreciate that like other cilia, photoreceptor sensory cilia (PSCs) consist of a basal body, axoneme, and specialized membrane domain. This is important because it connects IRDs at a mechanistic level to a larger class of systemic cilia disorders such as Bardet Biedl and Usher syndromes. From this connection, it is evident that many IRDs are caused by mutations in genes that encode proteins that are required for the function of PSCs and other cilia. The focus of Aim 1 will be continued investigations of the PSC protein RP1. Through studies of RP1 protein function in vitro and in vivo it has been shown that RP1 is a photoreceptor microtubule-associated protein (MAP) that is part of the photoreceptor axoneme, and is required for organization of outer segment structure. Recent data have lead to the hypothesis that RP1 is part of a complex of proteins that function in PSCs and other cilia to organize these structures. The investigations to test this hypothesis and study the pathogenesis of RP1 disease in Aim 1 are thus integrated with the studies of additional novel PSC proteins and genes that will be the focus of Aims 2 and 3. To facilitate work on RP1 and initiate studies of PSCs from a broader perspective a detailed proteomic analysis of mouse PSC complexes was performed. The PSC complex proteome identified by = 3 unique peptides contains 1968 proteins, including many novel PSC proteins. The locations of a subset of novel proteins in the PSC have been validated, confirming the accuracy of the proteome. The PSC complex proteome opens novel avenues for studies of how these cilia are built and maintained, and how these processes are disrupted in human disease. In Aim 2, the hypothesis that novel cilia proteins detected in the PSC complex proteome are important for PSC structure and function will be tested by studying a selected subset of novel PSC proteins. In Aim 3, the hypothesis that genes that encode novel PSC complex proteins are good candidate IRD disease genes will be tested by screening the genes that encode functionally validated PSC proteins for mutations that cause recessive and dominant IRDs.